Design of silicon micro‐resonators with low mechanical and optical losses for quantum optics experiments

The interaction of the radiation pressure with micro-mechanical oscillators is earning a growing inter- est for its wide-range applications and for fundamental research. In this contribution we describe the fabrica- tion of a family of opto-mechanical devices specifically designed to ease the detection of ponderomotive squeez- ing and of entanglement between macroscopic objects and light. These phenomena are not easily observed, due to the overwhelming effects of classical noise sources of ther- mal origin with respect to the weak quantum fluctuations of the radiation pressure. a low thermal noise background is required, together with a weak interaction between the micro-mirror and this background (i.e. high mechanical quality factors). In the development of our opto-mechan- ical devices, we heve explored an approach focused on a. Borrielli (*) · M. Bonaldi Institute of Materials for electronics and Magnetism, nanoscience -Trento-FBK Division, Via alla cascata 56/c, 38123 Trento, Tn, Italy e-mail: borrielli@fbk.eu a. Borrielli · M. Bonaldi · e. Serra · a. Pontin · G. a. Prodi Istituto nazionale di Fisica nucleare (InFn), Gruppo collegato di Trento, 38123 Trento, Tn, Italy e. Serra Interdisciplinary laboratory for computational Science (lISc), FBK-University of Trento, 38123 Trento, Tn, Italy e. Serra · G. Pandraud · P. M. Sarro Department of Microelectronics and computer, engineering /ecTM /DIMeS, Feldmanweg, 17, cT 2628 Delft, The netherlands a. Bagolini · P. Bellutti Microtechnology laboratory FBK-cMM, 38123 Trento, Tn, Italy relatively thick silicon oscillators with high reflectiv- ity coating. The relatively high mass is compensated by the capability to manage high power at low temperatures, owing to a favourable geometric factor (thicker connectors) and the excellent thermal conductivity of silicon crystals at cryogenic temperature. We have measured at cryogenic temperatures mechanical quality factors up to 105 in a micro-oscillator designed to reduce as much as possible the strain in the coating layer and the consequent energy dissi- pation. This design improves an approach applied in micro- mirror and micro-cantilevers, where the coated surface is reduced as much as possible to improve the quality factor. The deposition of the highly reflective coating layer has been carefully integrated in the micro-machining process to preserve its low optical losses.